Water heater has become one of the necessary household equipments, which can provide not only hot water for bath but also hot water for use in kitchen. However, no matter how the water heater is mounted, there is generally a water pipe between the water heater and each water consuming point. When there is no water demand at the water consuming point for a long time, the hot water in the water pipe will gradually cool down, and at the next time when there is a water demand at the water consuming point, especially at the time of the next bath, the water coming out first is the cold water. This not only causes great waste of water resources, but also brings uncomfortable bathing experience to the user. According to an estimation of investigations, in a residential building of ten floors, the length of the above mentioned pipeline is more than 5 meters in average. Take the diameter of the pipeline as 20 mm, the cold water discharged before having a bath each time by each household is about 1.6 litres. If each household uses the gas water heater for twice every day in average, then the water wasted by one household every year is about 1150 litres. If the whole residential building has 300 households, then the total amount of water wasted in one year reaches up to 345 tons.
In order to improve the degree of comfort of bathing for users while saving water resources, the researchers have tried to develop a technique of preheating and circulating the cold water in the pipeline using a circulating pump. The relevant prior art discloses a water heating system, which adds a circulating pump and a return pipeline inside the water heater, and thereby pumps the cooled water in the pipeline connecting the water consuming point and the water heater back to the water heater to be preheated, and in this way, the user can use hot water in time at the water consuming point. In the water heating system, a one-way valve is provided between the return pipeline and the hot water pipeline. In a case of normal water use, the one-way valve is in an off state, and only when the circulating pump is started to perform the preheating and circulation, the one-way valve is opened to communicate the return pipeline with the hot water pipeline, so as to finish the cyclic heating.
However, at present, the employed one-way valve usually uses a spring as a reset mechanism. When the water heater controls the circulating pump to open the one-way valve with a certain initial pressure, the spring will generally be compressed, and thus the resilience acting on a blocking mechanism will increase. In order to prevent the problem of pressure relief springback formed after the one-way valve is opened, the circulating pump needs to increase the pressure constantly to maintain the open state of the one-way valve, so as to ensure a stable return water circulation, and this has a high requirement for the circulating pump.
Besides, some times the water pressures of the cold water pipeline and the hot water pipeline will have fluctuations, which cause a situation where the pressure difference between two sides of the one-way valve is greater than its initial open pressure. Even if the pressure difference is maintained for a short time, the above one-way valve will still be opened in this case, which will cause cold and hot water to form series flow, resulting in a waste of heat energy.